1. Field of the Invention
The present invention relates to a structured document signature device, a structured document adaptation device and a structured document verification device.
2. Description of the Related Art
With reference to FIGS. 1 to 3, a description will be provided for a conventional digital signature method applied to a structured document.
FIG. 1 shows a format of a digital signature file in the conventional digital signature method applied to the structured document.
In FIG. 1, a “file signature code” indicates a digest value of an overall digital signature file, and a “depth code” indicates to what depth digest values of elements shall be included in the digital signature file. In addition, a plurality of “node signature codes” indicate digest values of the respective elements which are present in a range of depth specified by the depth code.
According to the conventional digital signature method applied to the structured document, the digest value of each element is concatenated with the digest value of an overall structured document, and a digital signature is added to a concatenated value.
For example, in an XML (eXtensible Markup Language) document (a structured document) shown in FIG. 2, when digest values D1 to D7 of the respective elements (e.g. <Document>) are calculated and the conventional digital signature method applied to the structured document is adapted to the digest values, an XML document with the digital signature shown in FIG. 3 is obtained.
In FIG. 3, the authenticity of the overall XML document shown in FIG. 2 can be verified by the digest value D1 of the element “<Document>”, and the authenticity of each element of the XML document can be verified by the digest value D2 of an element “<Chapter1>”, the digest value D3 of an element “<Section1-1> m11 </Section1-1>” and the like.
In this manner, the conventional digital signature method applied to the structured document can detect not only a modification of the overall structured document, but also a modification of each element forming the structured document.
In recent years, various structured documents represented by XML documents have been used in various services realized in a wide area network such as the Internet.
For example, a Web service, which is one of the most typical services, provides multimedia contents by use of a structured document (an HTML document) written in the HTML.
In addition, when a structured document written in an XML-compliant language which is termed as “SMIL” is used, not only a moving image and a sound can be delivered, but also a combination of various multimedia contents such as an animation, a still image and a text can be delivered.
In this manner, multimedia contents have been delivered in the form of structured documents in an increasing number of occasions. Hereinafter, when a structured document is referred to, it is assumed that the structured document includes multimedia contents.
On the other hand, as one of technologies for delivering multimedia contents, attention has been paid to a technology of adapting a structured document concerned with a service to be provided, in response to a user's environments (processing capabilities of a terminal device and a network, the user's location, time and the like) and the user's status (the user's age, affiliation, and license).
When a structured document is intended to be adapted, each element forming the structured document is an object to be adapted.
In this manner, when a provider intends to provide a digital signature to a structured document to be adapted, and when the digital signature is added to the digest value of the overall structured document in the same way as the conventional digital signature method applied to the structured document, the structured document is modified by the adaptation. Consequently, the authenticity of the structured document received can not be verified in a receiving terminal.
With regard to such a problem, according to the conventional digital signature method applied to the structured document, the digest value of each element is concatenated with the digest value of the overall structured document, and a digital signature is added to the concatenated values.
As a result, in a receiving terminal, the authenticity of each element can be verified. For this reason, the authenticity of an element which has not been adapted can be verified. For example, even if the value of an element is deleted, the authenticities of the other elements can be verified in a receiving terminal.
However, according to the conventional digital signature method applied to the structured document, nothing but the authenticity of an unadapted element can be verified, there is a problem in that it can not be verified whether or not the adaptation has been actually permitted by the provider of the structured document.
In addition, according to the conventional digital signature method applied to the structured document, the adaptation can be performed when the value of an element is deleted.
However, in a case where the adaptation is intended to be performed when an element itself is added, there is a disadvantage in that, if it is not clear whether or not the element has been added, the authentication of a digital signature which has been added by the sender can not be verified in the receiving terminal.
Furthermore, in the conventional digital signature method applied to the structured document, there is a disadvantage in that, if an element which has been added is deleted later, this fact can not be detected.